Now, for something completely different. Heck, I don’t even have a category for this one. I don’t typically post about auto repairs, but my post about my Coleman backpacking stove repair draws some unexpected interest, so I thought others may find this helpful.
My 11 year old Chevy Avalanche, with the 5.3L engine and 158,000 miles was having trouble running smoothly after a start in cold weather. I did some research online and there were several opinions. Maybe it was the throttle position sensor or mass airflow sensor and I think a few other suggestions. Then, I read a post by someone who described some symptoms which matched, in more detail, my symptoms. The truck started fine and idled high, as expected for about 15 seconds, then it sputtered and knocked . . . sounded like it was either going to throw a rod or just die out altogether. After about a minute or so of this torture (I never timed it) it just smoothed out and ran perfectly.
The problem, according to someone who posted a reference to a Technical Service Bulletin, was that sometime after 100,000 miles the intake manifold gasket begins to leak and needs to be replaced. I did a little checking around and picked one up from the local auto parts store.
I removed the intake manifold, which isn’t all that difficult on these newer vehicles. In the old days car engines had cast iron everything so, it seemed every bolt was rusted tight, and if you could get the bolts loose without breaking them off you considered yourself lucky. The most difficult step these days seems to be figuring out how the wiring connectors are locked to their respective sensor or fuel injector. You may recall the recent GM problem with the ignition key/switch not remaining in the “On” state under certain conditions, so it is clear why they are so tricky to remove from critical things like the electronic throttle motor /position sensor, or fuel injectors. So, if you give this a try, be patient and don’t break any of the connector locks. It took me 20 minutes to figure out how to get the throttle body motor/sensor disconnected and about the same to figure out how to remove the fuel injector connectors.
I released the fuel pressure by attaching a fuel pressure gauge to the fuel rail connector and depressed the pressure release button. Then I removed the fuel lines using the $8 plastic tools available at the auto parts store. The two lines are different sizes so get the two-size GM set.
The new manifold gasket was a little more stout than the original and nearly twice the price, so I’m hoping that it was the good choice. I packed paper towels into the cylinder head intake openings and cleaned all of the baked-on oil from the cylinder heads. Then I vacuumed off the mess, removed the towels and placed the new gasket on the engine. The original type was all plastic and clips to the intake manifold, but this one has metal spacers and is installed a little differently.
Reversing all my steps I re-installed the intake manifold, fuel lines, throttle body, and all of the wiring. I started it up and everything worked fine. Now, I need a cold morning. This morning was a cold morning in Colorado, but I’m not sure it was cold enough. The truck ran fine. Tonight it is supposed to be in the 20s so tomorrow morning should be a good test. Hopefully, it runs great.
UPDATE November 11th, 2014: The Avalanche sat for the last 24 hours at 20 degrees F or colder. I just went outside and it is 15 degrees. I started it up an it ran fine all the way until the engine was warm. It appears that the manifold gasket was indeed the problem as I have had no other service performed on the engine since the gasket change (except for oil, of course).
Thanks for visiting my blog.